U.S. patent application number 13/045208 was filed with the patent office on 2011-09-15 for system, method, and apparatus for controlling an aftertreatment system having a particulate filter and a rich nox conversion device.
Invention is credited to Marten H. Dane, Timothy R. Frazier, Samuel C. Geckler, Govindarajan Kothandaraman, Aleksey Yezerets.
Application Number | 20110219746 13/045208 |
Document ID | / |
Family ID | 44558607 |
Filed Date | 2011-09-15 |
United States Patent
Application |
20110219746 |
Kind Code |
A1 |
Yezerets; Aleksey ; et
al. |
September 15, 2011 |
SYSTEM, METHOD, AND APPARATUS FOR CONTROLLING AN AFTERTREATMENT
SYSTEM HAVING A PARTICULATE FILTER AND A RICH NOX CONVERSION
DEVICE
Abstract
A system includes an internal combustion ignition engine with an
exhaust gas flow, a particulate filter in the exhaust gas flow, a
NO.sub.x reduction catalyst in the exhaust gas flow downstream of
the particulate filter, a first oxygen sensor coupled to the
exhaust gas flow downstream of the NO.sub.x reduction catalyst, and
a second oxygen sensor coupled to the exhaust gas flow between the
particulate filter and the NO.sub.x reduction catalyst. A
controller includes an exhaust conditions module that interprets a
first oxygen signal from the first oxygen sensor and a second
oxygen signal from the second oxygen sensor and a combustion
control module that commands a high engine-out air-fuel ratio when
the first oxygen signal indicates a low oxygen content and commands
a low engine-out air-fuel ratio when the first oxygen signal
indicates a high oxygen content.
Inventors: |
Yezerets; Aleksey;
(Columbus, IN) ; Frazier; Timothy R.; (Columbus,
IN) ; Dane; Marten H.; (Greenwood, IN) ;
Geckler; Samuel C.; (Columbus, IN) ; Kothandaraman;
Govindarajan; (Columbus, IN) |
Family ID: |
44558607 |
Appl. No.: |
13/045208 |
Filed: |
March 10, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61312884 |
Mar 11, 2010 |
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Current U.S.
Class: |
60/274 ;
60/285 |
Current CPC
Class: |
F02D 41/1454 20130101;
F01N 2550/04 20130101; Y02T 10/24 20130101; Y02T 10/47 20130101;
Y02T 10/12 20130101; F02D 41/1408 20130101; Y02T 10/22 20130101;
F01N 11/005 20130101; F01N 9/002 20130101; F02D 41/029 20130101;
Y02T 10/40 20130101; F01N 3/035 20130101; F01N 2560/025 20130101;
F01N 3/101 20130101; F01N 2900/1602 20130101; F02D 2200/0812
20130101; F01N 2900/0416 20130101; F01N 2900/1606 20130101; F01N
11/007 20130101; F02D 2200/0802 20130101; F02D 41/1441 20130101;
F02D 41/146 20130101 |
Class at
Publication: |
60/274 ;
60/285 |
International
Class: |
F01N 3/035 20060101
F01N003/035; F01N 3/18 20060101 F01N003/18 |
Claims
1. A system, comprising: an internal combustion engine producing an
exhaust gas flow; a particulate filter disposed in the exhaust gas
flow; a NO.sub.x reduction catalyst disposed in the exhaust gas
flow downstream of the particulate filter; a controller comprising:
an exhaust conditions module structured to interpret a particulate
loading value for the particulate filter and a temperature of the
particulate filter; a filter requirements module structured to
determine an excess oxygen amount in response to the particulate
loading value and the temperature of the particulate filter; and a
combustion control module structured to command an engine-out
air-fuel ratio in response to the excess oxygen amount; and wherein
the internal combustion engine is responsive to the commanded
engine-out air-fuel ratio.
2. The system of claim 1, wherein the filter requirements module is
further structured to interpret the excess oxygen amount as zero in
response to one of the temperature of the particulate filter being
lower than an oxidation threshold temperature and the particulate
loading value for the particulate filter being lower than a
particulate oxidation threshold.
3. The system of claim 1, wherein the internal combustion engine is
a spark-ignited stoichiometric engine, and wherein the NO.sub.x
reduction catalyst is a three-way catalyst.
4. The system of claim 3, wherein the combustion control module is
further structured to command the engine-out air-fuel ratio in
response to the excess oxygen amount by oscillating the engine-out
air-fuel ratio between a lean value and a rich value averaged to
the excess oxygen amount.
5. The system of claim 4, wherein the filter requirements module is
further structured to interpret the excess oxygen amount as zero in
response to one of the temperature of the particulate filter being
lower than an oxidation threshold temperature and the particulate
loading value for the particulate filter being lower than a
particulate oxidation threshold.
6. The system of claim 5, wherein the filter requirements module is
further structured to determine the excess oxygen amount as a
positive value in response to the temperature of the particulate
filter being higher than the oxidation threshold temperature.
7. The system of claim 4, wherein the filter requirements module is
further structured to determine the excess oxygen amount as a
positive value in response to the particulate loading value being
greater than a particulate oxidation threshold.
8. The system of claim 4, wherein in response to the particulate
loading value being lower than a regeneration particulate loading
threshold, the combustion control module is further structured to
command the engine-out air-fuel ratio to a net stoichiometric
engine-out air-fuel ratio.
9. The system of claim 8, wherein the combustion control module is
further structured to command the engine-out air-fuel ratio as a
net lean engine-out air-fuel ratio in response to the particulate
loading value being greater than the regeneration particulate
loading threshold.
10. The system of claim 9, wherein the combustion control module is
further structured to command the engine-out air-fuel ratio such
that an oxygen signal from an oxygen sensor positioned between the
particulate filter and the NO.sub.x reduction catalyst is a net
stoichiometric signal in response to the particulate loading value
being greater than a regeneration particulate loading
threshold.
11. The system of claim 10, wherein the exhaust conditions module
is further structured to determine a nominal oxidation rate of the
particulate filter in response to the particulate loading value and
the temperature of the particulate filter; the system further
comprising a particulate filter diagnostic module structured to
determine a particulate filter diagnostic value in response to the
nominal oxidation rate, the oxygen signal from the oxygen sensor,
and an oxygen amount at a position upstream of the particulate
filter.
12. A method, comprising: determining a particulate loading value
and a temperature for a particulate filter; in response to the
particulate loading value and the temperature for the particulate
filter, determining an excess oxygen amount; and in response to the
excess oxygen amount, commanding an engine-out air-fuel ratio for
an engine.
13. The method of claim 12, wherein the determining the excess
oxygen amount comprises determining the excess oxygen amount such
that an exhaust gas flow downstream of the particulate filter is at
stoichiometric conditions.
14. The method of claim 13, wherein the stoichiometric conditions
comprise time-averaged stoichiometric conditions.
15. The method of claim 12, further comprising determining whether
particulate filter regeneration conditions are present, and
determining the excess oxygen amount to be zero in response to the
particulate filter regeneration conditions not being present.
16. The method of claim 15, wherein the determining whether
particulate filter regeneration conditions are present comprises
one of: determining that the particulate loading value is below a
particulate oxidation threshold; and determining that the
temperature for the particulate filter is below an oxidation
threshold temperature.
17. The method of claim 12, wherein the commanding the engine-out
air-fuel ratio for the engine comprises oscillating the engine-out
air-fuel ratio between a lean value and a rich value averaged to
the excess oxygen amount.
18. An apparatus, comprising: an exhaust conditions module
structured to interpret a particulate loading value for a
particulate filter and a temperature of the particulate filter; a
filter requirements module structured to determine an excess oxygen
amount in response to the particulate loading value and the
temperature of the particulate filter; and a combustion control
module structured to command an engine-out air-fuel ratio in
response to the excess oxygen amount.
19. The apparatus of claim 18, wherein the filter requirements
module is further structured to interpret the excess oxygen amount
as zero in response to one of the temperature of the particulate
filter being lower than an oxidation threshold temperature and the
particulate loading value for the particulate filter being lower
than a particulate oxidation threshold.
20. The apparatus of claim 18, wherein the combustion control
module is further structured to command the engine-out air-fuel
ratio in response to the excess oxygen amount by oscillating the
engine-out air-fuel ratio between a lean value and a rich value
averaged to the excess oxygen amount.
21. The apparatus of claim 18, wherein the exhaust conditions
module is further structured to interpret an oxygen signal from an
oxygen sensor positioned downstream of the particulate filter and
upstream of a NO.sub.x reduction catalyst, and wherein the
combustion control module is further structured to command the
engine-out air-fuel ratio such that the oxygen signal is a net
stoichiometric signal.
22. A system, comprising: an internal combustion engine producing
an exhaust gas flow; a particulate filter disposed in the exhaust
gas flow; a NO.sub.x reduction catalyst disposed in the exhaust gas
flow downstream of the particulate filter; a first oxygen sensor
operationally coupled to the exhaust gas flow downstream of the
NO.sub.x reduction catalyst; a second oxygen sensor operationally
coupled to the exhaust gas flow between the particulate filter and
the NO.sub.x reduction catalyst; and a controller comprising: an
exhaust conditions module structured to interpret a first oxygen
signal from the first oxygen sensor and a second oxygen signal from
the second oxygen sensor; and a combustion control module
structured to command a high engine-out air-fuel ratio in response
to the first oxygen signal indicating a low oxygen content out of
the NO.sub.x reduction catalyst and to command a low engine-out
air-fuel ratio in response to the first oxygen signal indicating a
high oxygen content out of the NO.sub.x reduction catalyst.
23. The system of claim 22, wherein the high engine-out air-fuel
ratio comprises a lambda value between 1.02 and 1.15, and wherein
the engine is a compression ignition engine.
24. The system of claim 22, wherein the high engine-out air-fuel
ratio comprises an air-fuel ratio to provide an oxygen fraction
between 0.25% and 9%, and wherein the engine is a compression
ignition engine.
25. The system of claim 22, wherein the combustion control module
is further structured to command the high engine-out air-fuel ratio
by controlling a combustion air-fuel ratio to a value between about
14.9 to about 16.3, and wherein the engine is a compression
ignition engine.
26. The system of claim 22, wherein the combustion control module
is further structured to command the high engine-out air-fuel ratio
by controlling a combustion air-fuel ratio to a value between about
14.9 to about 18, and wherein the engine is a compression ignition
engine.
27. The system of claim 22, wherein the combustion control module
is further structured to command the low engine-out air-fuel ratio
by controlling a combustion air-fuel ratio to a value between about
13.9 to about 14.7.
28. The system of claim 22, wherein the combustion control module
is further structured to command the low engine-out air-fuel ratio
by controlling a combustion air-fuel ratio to a value between about
14.4 to about 14.7.
29. The system of claim 22, further comprising a third oxygen
sensor operationally coupled to the exhaust gas flow upstream of
the particulate filter, wherein the exhaust conditions module is
further structured to interpret a third oxygen signal from the
third oxygen sensor, and wherein the combustion control module is
further structured to utilize the third oxygen signal as a feedback
parameter for the engine-out air-fuel ratio.
30. The system of claim 22, wherein the combustion control module
is further structured to command the high engine-out air-fuel ratio
in response to the first oxygen signal switching to indicating the
low oxygen content out of the NO.sub.x reduction catalyst, and to
command the low engine-out air-fuel ratio in response to the first
oxygen signal switching to indicating the high oxygen content out
of the NO.sub.x reduction catalyst.
31. The system of claim 30, wherein the combustion control module
is further structured to wait a first predetermined period of time
before commanding the high engine-out air-fuel ratio after the
first oxygen signal switches to indicating the low oxygen content
out of the NO.sub.x reduction catalyst, and to wait a second
predetermined period of time before commanding the low engine-out
air-fuel ratio after the first oxygen signal switches to indicating
the high oxygen content out of the NO.sub.x reduction catalyst.
32. The system of claim 22, wherein the combustion control module
commands the low engine-out air-fuel ratio by commanding a
combustion air-fuel ratio with less than or equal to a
stoichiometric amount of oxygen.
33. The system of claim 22, wherein the combustion control module
commands the high engine-out air-fuel ratio by commanding a
combustion air-fuel ratio with greater than a stoichiometric amount
of oxygen.
34. The system of claim 33, wherein the combustion control module
commands the high engine-out air-fuel ratio by commanding the
combustion air-fuel ratio such that an exhaust flow upstream of the
particulate filter includes an excess amount of oxygen and an
exhaust flow downstream of the particulate filter is about at a
stoichiometric ratio of oxygen.
35. The system of claim 34, further comprising a soot oxidation
estimation module structured to determine a soot oxidation rate in
the particulate filter, and wherein the combustion control module
commands the combustion air-fuel ratio in response to the soot
oxidation rate.
36. The system of claim 29, further comprising a diagnosis module
structured to determine a soot loading amount on the particulate
filter in response to a difference between the third oxygen signal
and the second oxygen signal.
37. The system of claim 36, wherein the diagnosis module is further
structured to determine the soot loading amount on the particulate
filter in response to an area between a third oxygen signal curve
and a second oxygen signal curve.
38. The system of claim 36, wherein the diagnosis module is further
structured to determine a first oxygen storage parameter in
response to an area between a second oxygen signal curve and a
first oxygen signal curve during a period where the combustion
control module is commanding the high engine-out air-fuel
ratio.
39. The system of claim 36, wherein the diagnosis module is further
structured to determine a second oxygen storage parameter in
response to an area between a first oxygen signal curve and a
second oxygen signal curve during a period where the combustion
control module is commanding the low engine-out air-fuel ratio.
40. A method, comprising: determining an first oxygen content in an
exhaust stream at a position downstream of a NO.sub.x reduction
catalyst with a first oxygen sensor; determining a second oxygen
content in the exhaust stream at a position downstream of a
particulate filter and upstream of the NOx reduction catalyst with
a second oxygen sensor; and operating an internal combustion engine
in response to the first oxygen content and the second oxygen
content, wherein the operating is performed to provide
stoichiometric conditions for the second oxygen content and excess
oxygen at the first oxygen content.
41. The method of claim 40, wherein the first oxygen sensor
comprises an oxygen sensor, a switching lambda sensor, a wide-range
lambda sensor, and/or a NO.sub.x sensor capable of providing oxygen
information.
42. The method of claim 40, further comprising determining a third
oxygen content at a position upstream of the particulate filter
with one of a third oxygen sensor and a virtual calculation of an
engine-out air-fuel ratio.
43. The method of claim 42, further comprising determining at least
one of a soot oxidation rate and an amount of soot stored on the
particulate filter according to the third oxygen content compared
to the second oxygen content.
44. The method of claim 43, wherein determining the at least one of
the soot oxidation rate and the amount of soot stored on the
particulate filter comprises determining an area between a curve of
third oxygen content and a curve of the second oxygen content, and
performing one of plotting and integrating the area against an
independent variable.
45. The method of claim 43, wherein determining the at least one of
the soot oxidation rate and the amount of soot stored on the
particulate filter comprises determining at least one parameter
selected from the parameters consisting of an average distance
between a curve of the third oxygen content and a curve of the
second oxygen content, a maximum distance between a curve of the
third oxygen content and a curve of the second oxygen content, and
a meaningful statistical comparison between a curve of the third
oxygen content and a curve of the second oxygen content.
46. The method of claim 40, wherein the internal combustion engine
is a compression ignition engine.
47. The method of claim 40, further comprising switching the
combustion to a high engine-out air-fuel ratio in response to the
first oxygen content indicating a low value.
48. The method of claim 40, further comprising switching the
combustion to a low engine-out air-fuel ratio in response to the
first oxygen content indicating a high value.
49. The method of claim 42, further comprising determining a
difference between the second oxygen content and the third oxygen
content, and controlling a soot oxidation rate on the particulate
filter by reducing the soot oxidation rate in response to the
difference between the second oxygen content and the third oxygen
content being greater than a high oxidation rate threshold, and
increasing the soot oxidation rate in response to the difference
between the second oxygen content and the third oxygen content
being less than a low oxidation rate threshold.
50. The method of claim 40, further comprising performing an
onboard diagnostic (OBD) check on the particulate filter, wherein
the performing the OBD check comprises checking the particulate
filter against performance criteria, wherein the performance
criteria includes an ability of the particulate filter to trap and
oxidize soot, and providing a diagnostic value in response to the
performance criteria.
51. The method of claim 40, further comprising performing an
onboard diagnostic (OBD) check on the NO.sub.x reduction catalyst,
wherein the performing the OBD check comprises checking the
NO.sub.x reduction catalyst against performance criteria, wherein
the performance criteria includes an ability of the NO.sub.x
reduction catalyst to store and release oxygen, and providing a
diagnostic value in response to the performance criteria.
Description
RELATED APPLICATIONS
[0001] This application is related, and claims the benefit of, U.S.
Provisional Patent Application 61/312,884 entitled "System, Method,
and Apparatus for Operating a Compression Ignition Engine at
Stoichiometric Conditions," which is incorporated herein by
reference for all purposes.
BACKGROUND
[0002] The present application relates to operating an internal
combustion engine at or near stoichiometric conditions, and further
relates to regenerating an aftertreatment system and other
challenges related thereto. The engine may be a spark ignited or
compression ignition engine. Aftertreatment systems are required to
bring emissions into compliance for many engine applications, and
many aftertreatment systems require accurate control of air-fuel
ratios to properly function and to regenerate. Further,
regeneration of some aftertreatment system components in the
absence of excess oxygen can be challenging. Accordingly, there is
a demand for further improvements in this area of technology.
[0003] In other examples, the present application relates to
controlling an aftertreatment system having a particulate filter
and a NO.sub.x conversion device that converts NO.sub.x under rich
or stoichiometric conditions. Many particulate filters require
excess oxygen to properly oxidize and remove trapped particulates.
NO.sub.x conversion devices that are not designed for lean
operation have limited NO.sub.x conversion when oxygen levels are
significantly higher than stoichiometric oxygen levels.
Accordingly, operational challenges are presented in an
aftertreatment system including a particulate filter and a NO.sub.x
conversion device that is not designed for lean operation.
SUMMARY
[0004] One embodiment is a unique method to control an
aftertreatment device having a particulate filter upstream of a
rich NO.sub.x conversion device. Further embodiments, forms,
objects, features, advantages, aspects, and benefits shall become
apparent from the following description and drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0005] FIG. 1 is a schematic diagram of a system for operating a
compression ignition engine at stoichiometric conditions.
[0006] FIG. 2 is an illustration of air-fuel ratios at various
times during operation of a compression ignition engine at
stoichiometric conditions.
[0007] FIG. 3 is a schematic diagram of a controller that
functionally executes certain operations for operating a
compression ignition engine at stoichiometric conditions.
[0008] FIG. 4 is a schematic flow diagram of a procedure for
operating a compression ignition engine at stoichiometric
conditions.
[0009] FIG. 5 is a schematic diagram of a system for control of an
aftertreatment system including a particulate filter and a rich
NO.sub.x conversion device.
[0010] FIG. 6 is a schematic diagram of a controller that
functionally executes certain operations for controlling an
aftertreatment system including a particulate filter and a rich
NO.sub.x conversion device.
[0011] FIG. 7 depicts illustrative data showing a lambda value
upstream and downstream of a particulate filter.
DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0012] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated in the drawings and specific language will
be used to describe the same. It will nevertheless be understood
that no limitation of the scope of the invention is thereby
intended, and any alterations and further modifications in the
illustrated embodiments, and any further applications of the
principles of the invention as illustrated therein as would
normally occur to one skilled in the art to which the invention
relates are contemplated and protected.
[0013] FIG. 1 is a schematic diagram of a system 100 for operating
a compression ignition engine at stoichiometric conditions. The
system 100 includes an internal combustion ignition engine 102 that
is designed to operate at stoichiometric conditions during at least
portions of the engine 102 operating period. An exemplary engine
102 is a compression ignition engine which may be a turbocharged
diesel engine, but may also be a direct injected gasoline engine or
any other engine operating as a compression ignition engine. The
exemplary system includes an oxidation catalyst 106, a particulate
filter 108, and a NO.sub.x reduction catalyst 110. The NO.sub.x
reduction catalyst 110 may be any NO.sub.x reduction catalyst known
in the art that operates at stoichiometric conditions during at
least a portion of the operating conditions of the catalyst, for
example the NO.sub.x reduction catalyst 110 may be a three-way
catalyst. The oxidation catalyst 106 may not be present in certain
embodiments. The particulate filter 108 traps a fraction of the
particulates in the exhaust flow 104, and the trapped particulates
are continuously or periodically oxidized on the particulate filter
108. The particulate filter 108 may be catalyzed or un-catalyzed,
and may be a wall flow filter or a flow-through filter.
[0014] The system 100 further includes a first oxygen sensor 114
operationally coupled to the exhaust flow 104 at a position
downstream of the NO.sub.x reduction catalyst 110. The system 100
further includes a second oxygen sensor 116 operationally coupled
to the exhaust flow 104 at a position downstream of the particulate
filter 108 and upstream of the NO.sub.x reduction catalyst 110. The
system 100 further includes a third oxygen sensor 118 upstream of
the particulate filter 108. The third oxygen sensor 118 may also be
positioned upstream of the oxidation catalyst 106, and in certain
embodiments the third oxygen sensor 118 may not be present or may
be a virtual sensor calculated from other parameters in the system
100. Each oxygen sensor 114, 116, 118 may be a lambda sensor, i.e.
a sensor that detects an air-fuel ratio in the exhaust flow 104 and
especially detects whether the exhaust flow 104 is relatively rich
or relatively lean at the position of the sensor 114, 116, 118. In
certain embodiments, a narrow band or "switching" lambda sensor may
be utilized for one or more of the oxygen sensors 114, 116, 118,
however a wide range lambda sensor is a preferred sensor and is
utilized in certain embodiments to support certain features
described herein, as will be understood to one of skill in the art.
Additionally, any oxygen sensor 114, 116, 118 may be a true oxygen
sensor (i.e. that determines the actual oxygen mole fraction or
mass fraction in the exhaust flow 104) or a NO.sub.x sensor that
also determines the oxygen fraction.
[0015] The system 100 further includes a controller 112 that
receives signals from the oxygen sensors 114, 116, 118. The
controller 112 communicates with any portion of the system 100,
including an engine controller (not shown) and any sensors or
actuators (not shown) to implement the functions of the controller
112 as described herein. The controller 112 may be part of a
processing subsystem, and includes an electronic processor and
memory of any known type, where the memory stores a computer
program, run-time variables, and information that is saved after
the controller 112 is powered down. The controller 112 may be a
single computer and/or part of a distributed computing subsystem,
where different computers communicate through datalinks, networks,
wireless communications, and the like. The controller 112 may be
included with an engine controller (not shown). Certain aspects of
the controller 112 may be implemented in hardware as well as
software, for example and without limitation a voltage parameter
may be converted in hardware before being processed by the
controller 112. Actuation by the controller 112 may occur by any
method understood in the art, including at least electronic,
datalink commands to a smart device or secondary controller,
pneumatic, and/or hydraulic actuation.
[0016] Referencing FIG. 3, a schematic diagram of a controller 112
that functionally executes certain operations for operating a
compression ignition engine at stoichiometric conditions is
illustrated. The controller 112 includes modules that functionally
execute the operations of the controller 112. The use of modules in
the description emphasizes the functional independence of the
operations of the controller 112, and the modules selected
illustrate one potential organization for the operations of the
controller 112. Some or all of the functions performed by any
module may be combined with the functions performed by other
modules, and some of the functions performed by any module may be
divided. A module may be a software element (e.g. as a function or
sub-routine) on a single controller, and/or may be divided among a
plurality of controllers. Some of the operations of a module may be
implemented in hardware rather than software. Certain modules may
not be present in certain embodiments of the system 100.
[0017] The controller 112 depicted in FIG. 3 includes an exhaust
conditions module 302, a combustion control module 304, a soot
oxidation estimation module 306, and a diagnosis module 308. The
exhaust conditions module 302 interprets a first oxygen signal 310,
a second oxygen signal 312, and may further interpret a third
oxygen signal 314. Interpreting a signal includes reading the
signal directly from a sensor 114, 116, 118, reading a value from a
sensor and converting the value to an oxygen description, reading a
software parameter having a value describing the oxygen signal 310,
312, 314, and/or receiving one or more of the oxygen signals 310,
312, 314 from a datalink or network.
[0018] The controller 112 further includes a combustion control
module 304 that commands a high engine-out air-fuel ratio 330 in
response to the first oxygen signal 310 indicating a low oxygen
content out of the NO.sub.x reduction catalyst 110. The combustion
control module 304 commands a low engine-out air-fuel ratio 332 in
response to the first oxygen signal 310 indicating a high oxygen
content out of the NO.sub.x reduction catalyst 110. The commanding
of the high engine-out air-fuel ratio 330 and/or the low engine-out
air-fuel ratio 332 may occur after a delay period, and may occur in
response to a switching of the first oxygen signal 310, for example
from a low oxygen content to a high oxygen content. In one example,
the combustion control module 304 waits a first predetermined
period of time before commanding the high engine-out air-fuel ratio
330 after the first oxygen signal 310 switches to indicating a low
oxygen content, and the combustion control module 304 waits a
second predetermined period of time before commanding the low
engine-out air-fuel ratio 332 after the first oxygen signal
switches to indicating a high oxygen content. The first and second
predetermined time periods may be selected to de-bounce the first
and second oxygen signals 310, 312, to ensure that certain
intermittent system dynamics do not prematurely trigger a switch
(e.g. a gear change by a vehicle operator triggering an unplanned
rich or lean slug through the exhaust flow 104), to prevent wear on
components due to rapid switching of operating modes, or to support
any other purposes understood in the art.
[0019] The high engine-out air-fuel ratio 330 includes, in certain
embodiments, an air-fuel ratio that provides an amount of excess
oxygen available for soot oxidation on the particulate filter 108.
The high engine-out air-fuel ratio 330 includes a lambda value
between about 1.02 and about 1.15, and includes a lambda of about
1.10 in certain embodiments. The high engine-out air-fuel ratio 330
includes an oxygen fraction between about 0.25% and about 9% in
certain embodiments. In one example, the combustion control module
304 commands the high engine-out air-fuel ratio 330 by commanding
the engine 102 to operate at a combustion air-fuel ratio between
about 14.9 to about 16.3, or from about 14.9 to about 18. The
described air-fuel ratio ranges may vary according to the fuel
formulation used in the system 100, as will be known to one of
skill in the art. The described ranges are for a system 100 having
a stoichiometric air-fuel ratio of about 14.8. The combustion
control module 304 may utilize the described ranges in controlling
engine combustion operation, or may select specific values within
the ranges.
[0020] In one example, the combustion control module 304 commands
the high engine-out air-fuel ratio 330 by initially commanding
about 10% excess oxygen during combustion (i.e. lambda 1.10 at the
third oxygen sensor 118 location, and/or combustion air-fuel ratio
around 16.3), and utilizes the second oxygen signal 312 as a
feedback parameter, targeting the exhaust flow 104 to have a lambda
at stoichiometric conditions (e.g. between about 0.99 and 1.01) at
the location of the second oxygen sensor 116. The combustion
control module 304 may utilize a proportional-integral,
proportional-integral-derivative, fuzzy logic, neural network, or
any other known control scheme to manipulate the combustion
air-fuel ratio until the target air-fuel ratio at the location of
the second oxygen sensor 116 is achieved.
[0021] The low engine-out air-fuel ratio 332 includes, in certain
embodiments, an air-fuel ratio that provides a slightly rich
condition the particulate filter 108. The low engine-out air-fuel
ratio 332 includes a lambda value between about 0.95 and about
1.00, and includes a lambda of about 0.98 in certain embodiments.
In one example, the combustion control module 304 commands the low
engine-out air-fuel ratio 332 by commanding the engine 102 to
operate at a combustion air-fuel ratio between about 13.9 to about
14.7, or from about 14.4 to about 14.7. The described air-fuel
ratio ranges may vary according to the fuel formulation used in the
system 100, as will be known to one of skill in the art. The
described ranges are for a system 100 having a stoichiometric
air-fuel ratio of about 14.8. The combustion control module 304 may
utilize the described ranges in controlling engine combustion
operation, or may select specific values within the ranges.
[0022] In one example, the combustion control module 304 commands
the low engine-out air-fuel ratio 332 by initially commanding about
2% oxygen shortage during combustion (i.e. lambda 0.98 at the third
oxygen sensor 118 location, and/or combustion air-fuel ratio around
14.4), and utilizes the second oxygen signal 312 as a feedback
parameter, targeting the exhaust flow 104 to have a lambda at
stoichiometric conditions (e.g. between about 0.99 and 1.01) at the
location of the second oxygen sensor 116. The combustion control
module 304 may utilize a proportional-integral,
proportional-integral-derivative, fuzzy logic, neural network, or
any other known control scheme to manipulate the combustion
air-fuel ratio until the target air-fuel ratio at the location of
the second oxygen sensor 116 is achieved.
[0023] The third oxygen signal 314 may further be utilized by the
combustion control module 304 as a feedback parameter for
controlling the engine-out air-fuel ratio. For example, the
combustion control module 304 may command parameters (fuel rate,
turbocharger flow rate and/or position, exhaust gas recirculation
flow rates, etc.) to achieve a specified air-fuel ratio, and
utilize the third oxygen signal 314 to determine whether the
specified air-fuel ratio is achieved. The combustion control module
304 may utilize a proportional-integral,
proportional-integral-derivative, fuzzy logic, neural network, or
any other known control scheme to manipulate the combustion
parameters until the specified air-fuel ratio at the location of
the third oxygen sensor 118 is achieved.
[0024] The controller 112 further includes a soot oxidation
estimation module 306 that determines a soot oxidation rate 316 in
the particulate filter 108. The combustion control module 304 may
further command the combustion air-fuel ratio in response to the
soot oxidation rate 316. In one example, the combustion control
module 304 limits oxygen to avoid exceeding a designed maximum soot
oxidation rate 316. The soot oxidation estimation module 306 may
determine the soot oxidation rate 316 by determining a second-third
oxygen signal difference 208. Referencing FIG. 2, the difference
208 between a third oxygen signal curve 206 and a second oxygen
signal curve 204 is related to the soot oxidation rate 316 on the
particulate filter 108 at a specific time.
[0025] The controller 112 further includes a diagnosis module 308.
In certain embodiments, the diagnosis module determines a soot
loading amount 318 on the particulate filter 108. In one example,
the diagnosis module 308 determines the soot loading amount 318 in
response to the difference 208 between a third oxygen signal curve
206 and a second oxygen signal curve 204, for example a highest
difference 208 observed during a high engine-out air-fuel ratio 330
event and/or an average difference 208 observed during the high
engine-out air-fuel ratio 330 event. In another example, the
diagnosis module 308 determines the soot loading amount 318 in
response to an area 214 between the third oxygen signal curve 206
and a second oxygen signal curve 204 during the high engine-out
air-fuel ratio 330 event. The soot loading amount 318 can be
published to the system 100, utilized in various diagnostics (e.g.
to determine whether ongoing soot regeneration is successful),
utilized to calibrate a soot oxidation model, or for any other
purpose understood in the art. In certain embodiments, the soot
oxidation rate 316 and/or soot loading amount 318 are utilized in
performing a particulate filter on-board diagnostics (OBD) 334
test.
[0026] In certain embodiments, the diagnosis module 308 determines
a first oxygen storage parameter 326 in response to the difference
210 between a second oxygen signal curve 204 and a first oxygen
signal curve 202, for example a highest difference 210 observed
during a high engine-out air-fuel ratio 330 event and/or an average
difference 210 observed during the high engine-out air-fuel ratio
330 event. In another example, the diagnosis module 308 determines
the first oxygen storage parameter 326 in response to an area 216
between the second oxygen signal curve 204 and the first oxygen
signal curve 202 during the high engine-out air-fuel ratio 330
event. The first oxygen storage parameter 326 can be published to
the system 100, utilized in various diagnostics (e.g. to determine
whether the NO.sub.x reduction catalyst 110 remains effective),
utilized to calibrate NO.sub.x reduction catalyst degradation
model, or for any other purpose understood in the art. In certain
embodiments, the first oxygen storage parameter 326 is utilized in
performing a NO.sub.x reduction catalyst OBD 336 test.
[0027] In certain embodiments, the diagnosis module 308 determines
a second oxygen storage parameter 328 in response to the difference
212 between a first oxygen signal curve 202 and a second oxygen
signal curve 204, for example a highest difference 212 observed
during a low engine-out air-fuel ratio 332 event and/or an average
difference 212 observed during the low engine-out air-fuel ratio
332 event. In another example, the diagnosis module 308 determines
the second oxygen storage parameter 328 in response to an area 218
between first oxygen signal curve 202 and a second oxygen signal
curve 204 during the low engine-out air-fuel ratio 332 event. The
second oxygen storage parameter 328 can be published to the system
100, utilized in various diagnostics (e.g. to determine whether the
NO.sub.x reduction catalyst 110 remains effective), utilized to
calibrate NO.sub.x reduction catalyst degradation model, or for any
other purpose understood in the art. In certain embodiments, the
first oxygen storage parameter 326 is utilized in performing a
NO.sub.x reduction catalyst OBD 336 test.
[0028] Referencing FIG. 2, three oxygen signal curves 202, 204, 206
are plotted illustrating a typical time segment of operation for
the system 100. At an early time, the first curve 202, indicating
oxygen content in the exhaust flow 104 downstream of the NO.sub.x
reduction catalyst 110, indicates a low oxygen content, and in
response the combustion control module 304 commands a high
engine-out air-fuel ratio 330. The third oxygen curve 206 responds
indicating a high oxygen content in the exhaust flow 104 upstream
of the particulate filter 108. The second oxygen curve 204
indicates a reduced oxygen content relative to the third oxygen
curve 206 due to soot oxidation on the particulate filter 108, but
the second oxygen curve 204 is still slightly lean (.lamda.=1.02)
but near stoichiometric conditions. For a period of time after the
third oxygen curve 206 is raised, the first oxygen curve 202 is
held near stoichiometric as the NO.sub.x reduction catalyst stores
oxygen. At a later point in time, oxygen breakthrough occurs and
the first oxygen curve 202 raises to approximately the same level
as the second oxygen curve 204. The combustion control module 304
may respond to the rise in the first oxygen curve 202 by commanding
the low engine-out air-fuel ratio 332 as shown in the illustration
of FIG. 2. Alternatively, the combustion control module 304 may
continue with a high engine-out air-fuel ratio 330 until the soot
on the particulate filter 108 is consumed (which may be indicated
by a rise in the second oxygen curve 204), although as the soot is
consumed the combustion control module 304 may lower the high
engine-out air-fuel ratio 330 from a nominal value to a lower but
still lean value--for example something lower than the .lamda.=1.10
illustrated in FIG. 2.
[0029] After the third oxygen curve 206 reaches the lower oxygen
content in response to the low engine-out air-fuel ratio 332 (e.g.
.lamda.=0.98 in the illustration), the second oxygen curve 204 also
reaches the lower oxygen content value. In certain embodiments,
some soot combustion may occur even at slightly rich conditions,
which may cause the second oxygen curve 204 to not exactly follow
the third oxygen curve 206, although this difference is not
important. The first oxygen curve 202 is maintained at or near
stoichiometric conditions for a period of time after the combustion
control module 304 commands the low engine-out air-fuel ratio 332
because the NO.sub.x reduction catalyst 110 has some stored oxygen
which is released maintaining stoichiometric conditions for a
period. The first oxygen curve 202 eventually drops as the stored
oxygen is depleted to about the level of the second oxygen curve
204. In response to the low third oxygen signal 314, the combustion
control module 304 returns to the high engine-out air-fuel ratio
330. Operations described in reference to FIG. 2 are for
illustration only, and are not intended to be limiting.
[0030] The schematic flow diagram in FIG. 4 and related description
which follows provides an illustrative embodiment of performing a
procedure for operating a compression ignition engine at
stoichiometric conditions. Operations illustrated are understood to
be exemplary only, and operations may be combined or divided, and
added or removed, as well as re-ordered in whole or part, unless
stated explicitly to the contrary herein.
[0031] FIG. 4 is a schematic flow diagram of a procedure 400 for
operating a compression ignition engine at stoichiometric
conditions. The procedure 400 includes an operation 402 to
interpret oxygen signals 310, 312, 314 from one or more oxygen
sensors. The procedure 400 further includes an operation 404 to
determine oxygen signal curves 202, 204, 206 from the oxygen
signals 310, 312, 314. The procedure 400 includes an operation 406
to determine whether a first oxygen signal 310 indicates a high
oxygen content or a low oxygen content. In response to the first
oxygen signal 310 indicating a HIGH oxygen content, the procedure
400 includes an operation 416 to command a low engine-out air-fuel
ratio 332. In response to the first oxygen signal 310 indicating a
LOW oxygen content, the procedure 400 includes an operation 418 to
command a high engine-out air-fuel ratio 330, an operation 420 to
determine a soot oxidation rate 316, and an operation 422 to set
the high engine-out air-fuel ratio 330 to a value such that the
second oxygen signal 312 indicates a stoichiometric (or
approximately stoichiometric) oxygen content.
[0032] The procedure 400 further includes an operation 408 to
determine a soot loading amount, and an operation 410 to perform an
OBD operation on the particulate filter 108. The procedure 400
further includes an operation 412 to determine a first oxygen
storage parameter 326 and a second oxygen storage parameter 328,
and an operation 414 to perform a NO.sub.x reduction catalyst OBD
operation. The OBD operations include determining trip definitions,
setting fault indicators, incrementing and/or decrementing fault
conditions, and/or resetting fault conditions as will be understood
to one of skill in the art.
[0033] The OBD operations include providing a diagnostic value in
response to the performance criteria and the trip definition. For
example, an ability of the particulate filter to store and oxidize
NO.sub.x is determined according to the consumption of oxygen
across the particulate filter during operations at a temperature,
particulate loading, and oxygen concentration where oxidation is
expected. Where the oxidation rate is observed to occur at a rate
that is consistent with a large amount of soot on the particulate
filter, the ability of the particulate filter to trap a large
amount of soot is confirmed. Where significant soot oxidation is
observed, the ability of the particulate filter to trap a large
amount of soot is confirmed.
[0034] In another example of OBD operations, an ability of the
NO.sub.x reduction catalyst to store and release oxygen is
determined according to oxygen slip delay across the NO.sub.x
reduction catalyst after an increase in the oxygen inlet amount to
the NO.sub.x reduction catalyst. Similarly, the ability of the
NO.sub.x reduction catalyst to release oxygen is determined
according to continued oxygen release after a decrease in the
oxygen inlet amount to the NO.sub.x reduction catalyst. The amount
of oxygen storage and release can be compared to standardized or
expected oxygen storage and release characteristics, confirming
whether the NO.sub.x reduction catalyst is performing acceptably,
performing at a reduced capacity, and/or failed.
[0035] FIG. 5 is a schematic diagram of a system 500 for control of
an aftertreatment system including a particulate filter 108 and a
rich NO.sub.x conversion device 110. The system 500 includes an
internal combustion engine 102 that produces an exhaust gas flow
104, the particulate filter 108 disposed in the exhaust gas flow
104. The particulate filter 108 traps a portion of particulate
matter (e.g. soot) flowing in the exhaust gas flow 104. The
particulate matter is oxidized at a later operating time, in the
presence of oxygen (or other oxidizing exhaust gas constituent) and
sufficient temperature. The system 500 further includes a NO.sub.x
reduction catalyst 110 disposed in the exhaust gas flow downstream
of the particulate filter. The NO.sub.x reduction catalyst 110 is a
rich or stoichiometric operating NO reducing catalyst. Any NOx
reduction catalyst known in the art is contemplated herein,
including a lean NO.sub.x catalysts that is utilized to reduce
NO.sub.x in rich or stoichiometric conditions during at least a
portion of the operating conditions of the system. The engine 102
may be a compression ignition engine or a spark ignited engine. An
exemplary system includes a spark-ignited engine where the NO.sub.x
reduction catalyst 110 is a three-way catalyst.
[0036] The exemplary system 500 further includes a controller 112.
The controller 112 includes one or more modules that functionally
execute certain operations for controlling the aftertreatment
system having the particulate filter 108 and the NO.sub.x reduction
catalyst 110. An exemplary controller 112 includes an exhaust
conditions module, a filter requirements module, a combustion
control module, and in certain embodiments a particulate filter
diagnostic module.
[0037] An exemplary exhaust conditions module interprets a
particulate loading value for the particulate filter and a
temperature of the particulate filter. An exemplary filter
requirements module determines an excess oxygen amount in response
to the particulate loading value and the temperature of the
particulate filter. An exemplary combustion control module commands
an engine-out air-fuel ratio in response to the excess oxygen
amount, where the internal combustion engine is responsive to the
commanded engine-out air-fuel ratio. More detailed operations of
exemplary embodiment s of the controller 112 are described in the
section referencing FIG. 6 following.
[0038] FIG. 6 is a schematic diagram of a controller 112 that
functionally executes certain operations for controlling an
aftertreatment system including a particulate filter and a rich
NO.sub.x conversion device. The controller 112 is consistent with
one form of a controller 112 usable in system 500. The controller
112 includes an exhaust conditions module 302 that interprets a
particulate loading value 606 for a particulate filter and a
temperature of the particulate filter 608. The particulate loading
value 606 is a parameter descriptive of an amount of soot or
particulates presently on the particulate filter. Exemplary
particulate loading values 606 may be quantitative--e.g. grams of
soot stored on the particulate filter, and/or qualitative--e.g. an
indicator of whether the particulate filter includes enough
particulate matter that soot can presently be oxidized, and/or
enough particulate matter that a regeneration is desired or
required. The determination of a particulate loading value 606 is
understood in the art, and may be made from pressure differential
and flow estimations through the particulate filter 108, and/or
modeling of soot accumulation and oxidation in the particulate
filter 108.
[0039] The controller 112 further includes a filter requirements
module 602 that determines an excess oxygen amount 610 in response
to the particulate loading value 606 and the temperature of the
particulate filter 608. The excess oxygen amount 610 is an amount
of oxygen in the exhaust gas flow that exceeds a stoichiometric
oxygen amount. The excess oxygen amount 610 is available for
oxidation of soot in the particulate filter. The determination of
the excess oxygen amount 610 is based upon the rate of oxidation of
soot in the particulate filter, which is dependent upon the
temperature of the particulate filter and the amount of soot
present in the particulate filter. Higher values of the particulate
loading value 606 generally indicate a higher excess oxygen amount
610, and higher particulate filter temperature 608 values generally
indicate higher excess oxygen amounts 610.
[0040] In certain embodiments, the excess oxygen amount 610 is a
function of the particulate loading value 606 and the particulate
filter temperature 608. Additionally or alternatively, the excess
oxygen amount 610 may be a fixed value, or one of several discrete
values, that is selected based upon a cutoff or threshold value of
the particulate loading value 606 and/or the particulate filter
temperature 608.
[0041] The controller 112 further includes a combustion control
module 304 that commands an engine-out air-fuel ratio 612 in
response to the excess oxygen amount 610. An internal combustion
engine is responsive to the engine-out air-fuel ratio command 612.
In certain embodiments, the combustion control module 304 commands
the engine-out air-fuel ratio 612 in response to the excess oxygen
amount by oscillating the engine-out air-fuel ratio between a lean
value 620 and a rich value 622 averaged to the excess oxygen amount
610. For example, referencing FIG. 7, illustrative data 700 of a
first curve 704 showing the oxygen amount (shown as a .lamda.
value) at a position between the engine 102 and the particulate
filter 108, for example as determined by an oxygen sensor 118 in
FIG. 5. The curve 704 oscillates between a lean and rich condition,
above and below the stoichiometric condition 706, such that
averaged over time, the excess oxygen amount 610 is provided. In
certain embodiments, the second curve 702 showing the oxygen amount
at a position between the particulate filter 108 and the NO.sub.x
reduction catalyst 110 is averaged over time to a lower oxygen
amount than the first curve 704, and may be averaged to a
stoichiometric condition 706.
[0042] In certain embodiments, the exhaust conditions module 302
further interprets an oxygen signal 624 from an oxygen sensor
positioned downstream of the particulate filter and upstream of a
NO.sub.x reduction catalyst, and the combustion control module 304
further commands the engine-out air-fuel ratio such that the oxygen
signal 624 is a net stoichiometric signal. For example, the
controller 112 may utilize the oxygen signal 624 as a feedback
signal to trim the engine-out AFR command 612 such that the excess
oxygen amount 610 is the amount of oxygen consumed across the
particulate filter and the NO.sub.x reduction catalyst receives net
stoichiometric conditions. The term net stoichiometric, as utilized
herein, indicates that over a period of time, over a number of
execution cycles, or over some other accumulating independent
variable, the amount of oxygen approximates, approaches, and/or
progresses toward the amount of oxygen that is required to combust
hydrocarbons in the exhaust, or the amount of oxygen that produces
a .lamda. value of 1 from a switching or wide-range oxygen
sensor.
[0043] In certain embodiments, the filter requirements module 602
interprets the excess oxygen amount 610 as zero in response to the
temperature of the particulate filter 608 being lower than an
oxidation threshold temperature 614, and/or in response to the
particulate loading value 606 for the particulate filter being
lower than a particulate oxidation threshold 616. The particulate
oxidation threshold 616 is an amount of particulates on the
particulate filter that, at the present particulate filter
temperature 608, or at an assumed default particulate filter
temperature, is low enough that significant oxidation by oxygen
across the particulate filter is not expected to occur. The
oxidation threshold temperature 614 is a temperature of the
particulate filter 608 where oxidation of particulates on the
particulate filter by the oxygen-based oxidation mechanism is low
enough that significant consumption of oxygen across the
particulate filter is not expected to occur. Accordingly, where
significant consumption of oxygen is not expected to occur, in
certain embodiments, the filter requirements module 602 eliminates
the excess oxygen amount 610 such that the NO.sub.x reduction
catalyst does not receive a significantly lean exhaust flow due to
residual oxygen.
[0044] An alternative or additional embodiment includes the filter
requirements module 602 determining the excess oxygen amount 610 as
a positive value in response to the temperature 608 of the
particulate filter being higher than the oxidation threshold
temperature 614. Yet another alternative or additional embodiment
includes the filter requirements module 602 determining the excess
oxygen amount 610 as a positive value in response to the
particulate loading value 606 being greater than a particulate
oxidation threshold 616. In certain embodiments, the filter
requirements module 602 models an available rate of oxidation by
oxygen across the particulate filter that occurs under the present
conditions on the particulate filter, and provides the excess
oxygen amount 610 based upon the available rate of oxidation, where
the excess oxygen amount 610 is the available rate or a fraction
thereof.
[0045] An exemplary controller 112 includes the combustion control
module 304 commanding the engine-out air-fuel ratio 612 to a net
stoichiometric engine-out air-fuel ratio in response to the
particulate loading value 606 being lower than a regeneration
particulate loading threshold 618. For example, although the
combination of the particulates available on the particulate filter
and the temperature 608 of the particulate filter may be
sufficiently high to produce some oxidation by oxygen, the overall
soot loading on the particulate filter may be low enough that
consumption of soot at the present time is not required or desired.
Accordingly, the combustion control module 304 provides a net
stoichiometric engine-out air-fuel ratio instead of the net excess
oxygen amount 610. Additionally or alternatively, the combustion
control module 304 commands the engine-out air-fuel ratio 612 as a
net lean engine-out air-fuel ratio in response to the particulate
loading value 606 being greater than the regeneration particulate
loading threshold 618.
[0046] In one form, the controller 112 includes the exhaust
conditions module 302 determining a nominal oxidation rate 628 of
the particulate filter in response to the particulate loading value
606 and the temperature 608 of the particulate filter. The nominal
oxidation rate 628 of the particulate filter is the rate of
oxidation by the oxygen mechanism (e.g. not including oxidation of
soot by NO.sub.2). The nominal oxidation rate 628 may be determined
from a model and/or determined according to an empirically
determined rate based upon the present operating conditions of the
engine and aftertreatment system. The controller 112 further
includes a particulate filter diagnostic module 604 that determines
a particulate filter diagnostic value 630 in response to the
nominal oxidation rate 628, the oxygen signal 624 from the oxygen
sensor, and an oxygen value 626 at a position upstream of the
particulate filter.
[0047] The oxygen value 626 describes an amount of oxygen in the
exhaust gas flow upstream of the particulate filter, and may be
measured by a sensor 118, and/or determined according to an
engine-out NO.sub.x map. In certain embodiments, the nominal
oxidation rate 628 and the engine-out NO.sub.x may be known at only
a few operating conditions, and the particulate filter diagnostic
module 604 determines the particulate filter diagnostic value 630
only at those few operating conditions. In certain embodiments, the
nominal oxidation rate 628 and/or engine-out NO.sub.x models may be
highly reliable only in a range of operating conditions, and the
particulate filter diagnostic module 604 determines the particulate
filter diagnostic value 630 only within that reliable range of
operating conditions.
[0048] The particulate filter diagnostic value 630 is a
quantitative or qualitative description of the oxidation
performance of the particulate filter relative to the nominal
oxidation rate 628 of the particulate filter. The particulate
filter diagnostic value 630 may be a percentage of the expected
oxidation rate, a description (e.g. PASS, FAIL, SUSPECT) of the
performance of the particulate filter, a fault counter that
increments and decrements based upon the performance of the
particulate filter relative to the nominal oxidation rate 628 of
the particulate filter, or other fault handling parameter
understood in the art. The particulate filter diagnostic module 604
may operate once per vehicle trip, engine operating cycle, or
according to some other schedule, and may be a part of a system
diagnostic or an OBD process.
[0049] The schematic flow descriptions which follow provide an
illustrative embodiment of performing a procedure for controlling
an aftertreatment system having a particulate filter and a NO.sub.x
reduction catalyst. Operations illustrated are understood to be
exemplary only, and operations may be combined or divided, and
added or removed, as well as re-ordered in whole or part, unless
stated explicitly to the contrary herein.
[0050] An exemplary procedure includes an operation to determine a
particulate loading value and a temperature for a particulate
filter, and in response to the particulate loading value and the
temperature for the particulate filter, an operation to determine
an excess oxygen amount. The procedure further includes, in
response to the excess oxygen amount, commanding an engine-out
air-fuel ratio for an engine. The exemplary procedure further
includes determining the excess oxygen amount by determining an
excess oxygen amount such that an exhaust gas flow downstream of
the particulate filter is at stoichiometric conditions. The
stoichiometric conditions, in one form, are time-averaged
stoichiometric conditions and/or net stoichiometric conditions. An
exemplary procedure further includes an operation to determine
whether particulate filter regeneration conditions are present, and
an operation to determine the excess oxygen amount to be zero in
response to the particulate filter regeneration conditions not
being present.
[0051] In certain embodiments, the procedure includes an operation
to determine whether particulate filter regeneration conditions are
present by determining that the particulate loading value is below
a particulate oxidation threshold, and/or by determining that the
temperature for the particulate filter is below an oxidation
threshold temperature. The operation to command the engine-out
air-fuel ratio includes, in one form, oscillating the engine-out
air-fuel ratio between a lean value and a rich value averaged to
the excess oxygen amount.
[0052] As is evident from the figures and text presented above, a
variety of embodiments according to the present invention are
contemplated.
[0053] One exemplary embodiment is a system including a compression
ignition engine producing an exhaust gas flow, a particulate filter
disposed in the exhaust gas flow, a NO.sub.x reduction catalyst
disposed in the exhaust gas flow downstream of the particulate
filter, a first oxygen sensor operationally coupled to the exhaust
gas flow downstream of the NO.sub.x reduction catalyst, a second
oxygen sensor operationally coupled to the exhaust gas flow between
the particulate filter and the NO.sub.x reduction catalyst, and a
controller having modules structured to functionally execute a
procedure for operating a compression ignition engine at a
stoichiometric condition. The controller includes an exhaust
conditions module and a combustion control module. In certain
embodiments, the controller further includes a soot oxidation
estimation module and a diagnosis module.
[0054] The exhaust conditions module interprets a first oxygen
signal from the first oxygen sensor and a second oxygen signal from
the second oxygen sensor. The combustion control module commands a
high engine-out air-fuel ratio in response to the first oxygen
signal indicating a low oxygen content out of the NOx reduction
catalyst and commands a low engine-out air-fuel ratio in response
to the first oxygen signal indicating a high oxygen content out of
the NO.sub.x reduction catalyst.
[0055] The high engine-out air-fuel ratio can include any value
over a stoichiometric value, and in certain embodiments includes a
lambda value between 1.02 and 1.15. In certain embodiments, the
high engine-out oxygen fraction includes an oxygen fraction between
0.25% and 9% in the post-combustion exhaust stream. In certain
embodiments, the combustion control module commands the high
engine-out air-fuel ratio by controlling a combustion air-fuel
ratio to a value between about 14.9 to about 16.3, and/or to a
value between about 14.9 to about 18.
[0056] The low engine-out air-fuel ratio can include any value
below a stoichiometric value, and in certain embodiments includes a
lambda value below about 0.99 or below about 0.98. In certain
embodiments, the combustion control module commands the low
engine-out air-fuel ratio by controlling a combustion air-fuel
ratio to a value between about 13.9 to about 14.7, and/or to a
value between about 14.4 to about 14.7.
[0057] Certain exemplary embodiments of the system include a third
oxygen sensor operationally coupled to the exhaust gas flow
upstream of the particulate filter, and the exhaust conditions
module interprets a third oxygen signal from the third oxygen
sensor. The combustion control module is further structured to
utilize the third oxygen signal as a feedback parameter for the
engine-out air-fuel ratio. In one example, the combustion control
module utilizes a feedforward model to estimate combustion
conditions required to achieve the target engine-out air-fuel
ratio, and trims the combustion conditions by determining an error
value between the measured engine-out air-fuel ratio and the target
engine-out air-fuel ratio.
[0058] The combustion control module may further command the high
engine-out air-fuel ratio in response to the first oxygen signal
switching to indicating a low oxygen content out of the NO.sub.x
reduction catalyst, and command the low engine-out air-fuel ratio
in response to the first oxygen signal switching to indicating a
high oxygen content out of the NO.sub.x reduction catalyst. In
certain embodiments, the combustion control module further waits a
first predetermined period of time before commanding the high
engine-out air-fuel ratio after the first oxygen signal switches to
indicating a low oxygen content out of the NO.sub.x reduction
catalyst, and waits a second predetermined period of time before
commanding the low engine-out air-fuel ratio after the first oxygen
signal switches to indicating a high oxygen content out of the
NO.sub.x reduction catalyst.
[0059] In certain embodiments, the combustion control module
commands the low engine-out air-fuel ratio by commanding a
combustion air-fuel ratio with less than or equal to a
stoichiometric amount of oxygen, and/or commands the high
engine-out air-fuel ratio by commanding a combustion air-fuel ratio
with greater than a stoichiometric amount of oxygen. The exemplary
combustion control module commands the high engine-out air-fuel
ratio by commanding the combustion air-fuel ratio such that the
exhaust flow upstream of the particulate filter includes an excess
amount of oxygen and the exhaust flow downstream of the particulate
filter is about at a stoichiometric ratio of oxygen. The system
further includes a soot oxidation estimation module that determines
a soot oxidation rate in the particulate filter, and the combustion
control module commands the combustion air-fuel ratio in response
to the soot oxidation rate.
[0060] The exemplary system includes a diagnosis module that
determines a soot loading amount on the particulate filter in
response to a difference between the third oxygen signal and the
second oxygen signal and /or in response to an area between a third
oxygen signal curve and a second oxygen signal curve. The diagnosis
module further determines a first oxygen storage parameter in
response to an area between a second oxygen signal curve and a
first oxygen signal curve during a period where the combustion
control module is commanding the high engine-out air-fuel ratio,
and determines a second oxygen storage parameter in response to an
area between a first oxygen signal curve and a second oxygen signal
curve during a period where the combustion control module is
commanding the low engine-out air-fuel ratio. In certain
embodiments, the diagnosis module further performs an on-board
diagnostic routine for the particulate filter and/or for the
NO.sub.x reduction catalyst.
[0061] Another exemplary embodiment is a method including operating
a compression ignition engine at stoichiometric combustion
conditions, and monitoring the oxygen content of exhaust gases at
various locations in the exhaust stream. The exhaust gases may be
monitored with oxygen sensors, including switching lambda sensors,
wide-range lambda sensors, oxygen sensors, and/or NO.sub.x sensors
that are also capable of providing oxygen information. The method
includes determining the oxygen content (or air-fuel ratio) at a
position downstream of a NO.sub.x reduction catalyst with a first
oxygen sensor and determining the oxygen content and/or air-fuel
ratio at a position downstream of a particulate filter and upstream
of the NO.sub.x reduction catalyst with a second oxygen sensor. The
method further includes determining the oxygen content (or air-fuel
ratio) at a position upstream of the particulate filter, either
with a third oxygen sensor and/or with a virtual calculation of the
engine out conditions.
[0062] The method further includes providing stoichiometric
conditions at the NO.sub.x reduction catalyst while providing
excess oxygen at the particulate filter to oxidize soot stored on
the particulate filter. In certain embodiments, the method includes
determining an oxidation rate of soot in the particulate filter,
and providing excess oxygen such that the remaining oxygen out of
the particulate filter leaves the exhaust gas entering the NO.sub.x
reduction catalyst at about stoichiometric conditions. In certain
embodiments, the method includes switching the combustion to a high
engine-out air-fuel ratio in response to the oxygen content
downstream of the NO.sub.x reduction catalyst indicating a low
value. The method can further include switching the combustion to a
low engine-out air-fuel ratio in response to the oxygen content
downstream of the NO.sub.x reduction catalyst indicating a high
value.
[0063] The method further includes determining a soot oxidation
rate and/or an amount of soot stored on the particulate filter. The
soot oxidation rate and the soot stored on the particulate filter
may be determined according to an air-fuel ratio upstream of the
particulate filter compared to an air-fuel ratio downstream of the
particulate filter. The comparison may include determining an area
between a curve of the air-fuel ratio upstream of the particulate
filter and the air-fuel ratio downstream of the particulate filter,
plotted or integrated against an independent variable such as time.
The comparison may include determining an average distance between
the curves, a maximum distance between the curves, or any other
meaningful statistical comparison between the curves.
[0064] The method further includes determining an oxygen storage
capacity of the NO.sub.x reduction catalyst. The oxygen storage
capacity may be determined according to an air-fuel ratio upstream
of the NO.sub.x reduction catalyst compared to an air-fuel ratio
downstream of the NO.sub.x reduction catalyst. The comparison may
include determining an area between a curve of the air-fuel ratio
upstream of the NO.sub.x reduction catalyst and the air-fuel ratio
downstream of the NO.sub.x reduction catalyst, plotted or
integrated against an independent variable such as time. The
comparison may include determining an average distance between the
curves, a maximum distance between the curves, or any other
meaningful statistical comparison between the curves.
[0065] In another embodiment, the method includes controlling a
soot oxidation rate on the particulate filter by determining a
difference in the oxygen concentration and/or lambda upstream of
the particulate filter and downstream of the particulate filter.
The soot oxidation rate is reduced if the oxygen concentration or
lambda difference is too great by reducing the engine-out air-fuel
ratio, and the soot oxidation rate is increased if the oxygen
concentration or lambda difference is too small.
[0066] In certain embodiments, the method includes performing an
onboard diagnostic (OBD) check on the particulate filter and/or the
NO.sub.x reduction catalyst. The OBD check includes defining a trip
event, checking the particulate filter and/or NO.sub.x reduction
catalyst against performance criteria, incrementing, decrementing,
and/or setting fault values and criteria, and any other OBD
operations known in the art, required by law, or available based
upon the descriptions herein. In certain embodiments, performance
criteria include the ability of the particulate filter to trap and
support oxidation of soot from the exhaust stream, and/or the
ability of the NO.sub.x reduction catalyst to store and release
oxygen.
[0067] The operations of the method may be executed by a computer
program product stored on a computer readable medium having coded
instructions that, when executed by a computer, cause the computer
to perform one or more functions of the method. Some functions of
the method may be performed in software or hardware. The computer
program product may be stored on a single computer readable medium
or may be distributed across multiple computers, which may be in
communication via datalinks, networks, and/or wireless
communications.
[0068] Yet another exemplary set of embodiments is a system
including an internal combustion engine that produces an exhaust
gas flow, a particulate filter disposed in the exhaust gas flow,
and a NO.sub.x reduction catalyst disposed in the exhaust gas flow
downstream of the particulate filter. The engine may be a
compression ignition engine or a spark ignited engine. An exemplary
system includes a spark-ignited engine where the NO.sub.x reduction
catalyst is a three-way catalyst.
[0069] The exemplary system further includes a controller, the
controller having an exhaust conditions module, a filter
requirements module, a combustion control module, and in certain
embodiments a particulate filter diagnostic module. An exemplary
exhaust conditions module interprets a particulate loading value
for the particulate filter and a temperature of the particulate
filter. An exemplary filter requirements module determines an
excess oxygen amount in response to the particulate loading value
and the temperature of the particulate filter. An exemplary
combustion control module commands an engine-out air-fuel ratio in
response to the excess oxygen amount, where the internal combustion
engine is responsive to the commanded engine-out air-fuel
ratio.
[0070] In certain embodiments, the filter requirements module
interprets the excess oxygen amount as zero in response to the
temperature of the particulate filter being lower than an oxidation
threshold temperature, and/or in response to the particulate
loading value for the particulate filter being lower than a
particulate oxidation threshold. Certain further embodiments
include the combustion control module commanding the engine-out
air-fuel ratio in response to the excess oxygen amount by
oscillating the engine-out air-fuel ratio between a lean value and
a rich value averaged to the excess oxygen amount.
[0071] An exemplary system further includes the filter requirements
module determining the excess oxygen amount as zero in response to
the temperature of the particulate filter being lower than an
oxidation threshold temperature, and/or the particulate loading
value for the particulate filter being lower than a particulate
oxidation threshold. An alternative or additional embodiment
includes the filter requirements module determining the excess
oxygen amount as a positive value in response to the temperature of
the particulate filter being higher than the oxidation threshold
temperature. Yet another alternative or additional embodiment
includes the filter requirements module determining the excess
oxygen amount as a positive value in response to the particulate
loading value being greater than a particulate oxidation
threshold.
[0072] Another exemplary system includes the combustion control
module commanding the engine-out air-fuel ratio to a net
stoichiometric engine-out air-fuel ratio in response to the
particulate loading value being lower than a regeneration
particulate loading threshold. Additionally or alternatively, the
combustion control module commands the engine-out air-fuel ratio as
a net lean engine-out air-fuel ratio in response to the particulate
loading value being greater than the regeneration particulate
loading threshold.
[0073] A still further embodiment includes the combustion control
module commanding the engine-out air-fuel ratio such that an oxygen
signal from an oxygen sensor positioned between the particulate
filter and the NO.sub.x reduction catalyst is a net stoichiometric
signal in response to the particulate loading value being greater
than a regeneration particulate loading threshold. Additionally or
alternatively, the exhaust conditions module determines a nominal
oxidation rate of the particulate filter in response to the
particulate loading value and the temperature of the particulate
filter. The exemplary system further includes a particulate filter
diagnostic module that determines a particulate filter diagnostic
value in response to the nominal oxidation rate, the oxygen signal
from the oxygen sensor, and an oxygen amount at a position upstream
of the particulate filter.
[0074] Another exemplary set of embodiments is a method, including
determining a particulate loading value and a temperature for a
particulate filter, and in response to the particulate loading
value and the temperature for the particulate filter, determining
an excess oxygen amount. The method further includes, in response
to the excess oxygen amount, commanding an engine-out air-fuel
ratio for an engine.
[0075] Additional or alternative operations of the method are
described as follows. An exemplary method includes determining the
excess oxygen amount by determining an excess oxygen amount such
that an exhaust gas flow downstream of the particulate filter is at
stoichiometric conditions. The stoichiometric conditions, in one
form, are time-averaged stoichiometric conditions. An exemplary
method further includes determining whether particulate filter
regeneration conditions are present, and determining the excess
oxygen amount to be zero in response to the particulate filter
regeneration conditions not being present.
[0076] In certain embodiments, the method includes determining
whether particulate filter regeneration conditions by determining
that the particulate loading value is below a particulate oxidation
threshold, and/or by determining that the temperature for the
particulate filter is below an oxidation threshold temperature. The
operation to command the engine-out air-fuel ratio includes, in one
form, oscillating the engine-out air-fuel ratio between a lean
value and a rich value averaged to the excess oxygen amount.
[0077] Yet another exemplary set of embodiments is an apparatus,
including an exhaust conditions module that interprets a
particulate loading value for a particulate filter and a
temperature of the particulate filter, a filter requirements module
that determines an excess oxygen amount in response to the
particulate loading value and the temperature of the particulate
filter, and a combustion control module that commands an engine-out
air-fuel ratio in response to the excess oxygen amount. In certain
embodiments, the the filter requirements module interprets the
excess oxygen amount as zero in response to one of the temperature
of the particulate filter being lower than an oxidation threshold
temperature and the particulate loading value for the particulate
filter being lower than a particulate oxidation threshold.
[0078] In certain embodiments, the combustion control module
commands the engine-out air-fuel ratio in response to the excess
oxygen amount by oscillating the engine-out air-fuel ratio between
a lean value and a rich value averaged to the excess oxygen amount.
An exemplary apparatus includes the exhaust conditions module
further interpreting an oxygen signal from an oxygen sensor
positioned downstream of the particulate filter and upstream of a
NO.sub.x reduction catalyst, where the combustion control module
further commands the engine-out air-fuel ratio such that the oxygen
signal is a net stoichiometric signal.
[0079] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only certain exemplary embodiments have been
shown and described and that all changes and modifications that
come within the spirit of the inventions are desired to be
protected. In reading the claims, it is intended that when words
such as "a," "an," "at least one," or "at least one portion" are
used there is no intention to limit the claim to only one item
unless specifically stated to the contrary in the claim. When the
language "at least a portion" and/or "a portion" is used the item
can include a portion and/or the entire item unless specifically
stated to the contrary.
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